The use of morphological and immunocytochemical techniques to examine protein trafficking, vesicle recycling, microfilament organization, signal transduction pathways and cell and organelle structure continues to comprise a large part of the work proposed by the individual projects in this Program Project renewal. The techniques required include conventional light and electron microscopy light and EM immunocytochemistry, laser confocal microscopy and digital fluorescence imaging, conventional freeze-fracture, ultracryomicrotomy, and real-time cell imaging. Special startup funds from MGH for the MGH-East facility originally enabled us to purchase excellent equipment that continues to form the nucleus of the Microscopy Core facility, but this sophisticated instrumentation is expensive in terms of dedicated supplies required and upkeep. This is reflected in the core supply budget and requested contributions towards selected service contracts. A major aim of the Core facility is to continually upgrade the equipment and the range of techniques that are available to users. Since the last competitive renewal, several major pieces of equipment have been added to the Core, which have improved and expanded the services available to the investigators of the Program Project. This equipment has been purchased using generous NIH support from a large equipment grant, other NIH funding, and continued Institutional support.